Do most dogs treat people based on their physical apparence?

I definitely believe that dogs can pick up on mannerisms of people, and I think it's a great question to bring up whether dogs judge by appearence of a person. I do think that dogs do a very quick analisys based on appearence and relate traits of individuals to behaviors. If you're a big person and the dog has had a previous negative experience where the dog was threatened by a person who was also big then the dog will relate that and feel threatened by you. And this goes for much more detailed features too, like hair and eye color, clothing, actions and gestures, any of these can set off a reaction from the dog based on its previous experience with people who have those features.